128538991 has 8 divisors (see below), whose sum is σ = 151967520. Its totient is φ = 106376928.

The previous prime is 128538979. The next prime is 128539001. The reversal of 128538991 is 199835821.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 128538991 - 2⁵ = 128538959 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (128538931) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 316396 + ... + 316801.

It is an arithmetic number, because the mean of its divisors is an integer number (18995940).

Almost surely, 2^128538991 is an apocalyptic number.

128538991 is a deficient number, since it is larger than the sum of its proper divisors (23428529).

128538991 is an equidigital number, since it uses as much as digits as its factorization.

128538991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 633233.

The product of its digits is 155520, while the sum is 46.

The square root of 128538991 is about 11337.5037375959. The cubic root of 128538991 is about 504.6748107389.

The spelling of 128538991 in words is "one hundred twenty-eight million, five hundred thirty-eight thousand, nine hundred ninety-one".